382 
EDWARD PHELPS ALLIS. 
antero-mesially to reach and penetrate the anterior portion of 
the musculus intermandibularis. On the other side of the 
head of this same specimen, what was apparently the corre- 
sponding branch was given off while the main nerve was on 
the internal surface of the intermandibularis, and, having 
perforated that muscle from within outward, it joined and 
anastomosed with the latero-sensory nerve that innervates 
the sense organs of the hyomandibular line. No branch was 
noticed later leaving the latero-sensory nerve to go to the 
musculus intermandibularis, but as the dissection was made 
without any thought of there being such a branch it is 
probable that it existed but was overlooked. No branch of 
the nervus trigeminus was found going to any part of the 
muscle-sheet in any of my specimens. Luther (1909) shows 
a branch of this latter nerve going to the anterior end of the 
muscle, but he considered it to probably be a sensory and not 
a motor nerve. 
The nervus hyoideus facialis must primarily have lain, in 
all the Selachii, along the anterior (external) surface of all 
the muscles it innervates that nre derived from the myotome 
of its own arch, that being the position in which all the 
branchial nerves are found, and it does actually lie external 
to the interhyoideus in all of the five specimens of Chlamydo- 
selachus above described. It, however, lies, in four of those 
five specimens, external to certain portions of the inter- 
mandibularis, but internal to certain other portions. If this 
intermandibularis muscle be developed from the myotome of 
the hyal arch, this difference in the relations of the nerve to 
the muscle can be naturally explained, as in the dorsal portion 
of the constrictor of this arch, by the assumption that certain 
of the fibres of the muscle, which were primarily inserted on 
the ceratohyal, had secondarily acquired insertion on the 
mandibula by passing external to the nerve as that nerve ran 
forward near the ventral (morphologically posterior) edge of 
the mandibula, while in other cases the muscle retained its 
primitive position internal (posterior) to the nerve. This 
explanation would, however, not apply if the intermandibu- 
